In an effort to increase drill bit life, coatings have been applied to the abrasive cutting media (e.g., diamonds) within drill bits. The diamond industry conventionally uses CVD (Chemical Vapor Deposition) or PVD (Physical Vapor Deposition) coatings to increase bond strength between the matrix of the bit and the abrasive cutting media (e.g., diamond). Conventionally, the most common coatings are Titanium, Chrome, Silicon, and Nickel. The CVD coatings are chemically applied, causing the metallic or semi-metallic coating to react with the diamond and create a strong carbide coating. Unfortunately, after the CVD coating is exposed to the atmosphere, it often forms an oxide layer on the surface of the coated diamond, limiting and weakening the chemical bonding with the matrix in the infiltration/sintering process. The PVD coatings do not form a carbide bond with the diamond; they only have a mechanical bond with the diamond, which is much weaker. In addition, similar to the CVD coatings, when the PVD coatings are exposed to the atmosphere, they can form an oxide layer on the surface of the coated diamond before forming a bond to the matrix/diamond, preventing a good bond to the matrix. Further, the CVD and PVD coatings are limited by the size of the diamonds; if the diamond is too small, the coatings cannot be applied effectively.
Multi-layered coatings have also been used. To apply such coatings, a carbide layer is formed using a CVD coating process, and then another layer is added to create a stronger bond between the carbide and the matrix. This creates a stronger coating, but the process is not economical due to the multi-step nature of the process and the expensive materials needed for the additional layers. For example, formation of multi-layered coatings in a CVD coating process conventionally requires multiple heating operations. In addition, the outermost (additional) layer will still form an oxide, thereby limiting the bond strength. Additionally, the smaller the diamonds within the drill bits, the more expensive and/or difficult to apply the multi-layer coatings become.
Thus, there is a need for less costly drill bits that have increased penetration rates and are more resistant to breaking down, thereby decreasing the amount of required rod tripping (due to the longer life of the bits) and increasing the amount of core per shift (due to increased penetration rates).